Process of treating copper ores by lixiviation.



20 simple, cheap, eflicient and exceedingly Vall 1' "No Drawing. 1

UNITED STA ES PATENT NInLs'c. onmsrnnsjan, or'saLr LAKE CITY, UTAH, Assmnoa or ONE-HALF 'ro J. E. BAR-LOW, or HABANA, UBA, AND O'NETHALF 'ro BIG INDIAN corrna co,

or UTAH.

To all whom z'tzmayconcem: 1: Be it known that I, NIELs Ci OHRISTEN-I sun, a citizen of the United States, residing 7 at Salt Lake City, in the county of Salt Lake kaiid State'of-Utah, have invented new and useful'lm provements, in Processes of Treat- .ing Copper Ores by "Lixiviation, of which the followingisa specification.

This lnvention'relates to the art of treating copper ore for'recovery of the copper,

more particularly to an'imp'roved process the di culties which have made failures of prior attempts to utilize a water solution of -80; on a commercial-scale for the treatment of oxidized copper ore, and thereby to make the use of this solvent possible in a .able-process.

The accompanying-drawing illustrates diagrammatical y the several. steps and apparatus employedin carrying out my inven-.

tion, the novel features of which are particularly pointed out in the claims at the end of the specification.

Prior to my invention, it has been generally known b that a water-so .ution of SO dissolves the oxidized "compounds of copper, and that, on

. boiling off the excess SO from the solution containing the copper, part of the copper is precipitated as the red cupro oupric sulfite,

CliSOQCliSO," and the remainder of the cop er is left in solution as copper sulfate, While. a number of attempts have been made to utilize these facts for the treatment of copper ore on a'commercial scale, they have all failed for'the reason that none of the vital elements andnone of the essential facts necessary. to the use ofSO soluelements andas aresult provides a process tion as asolvent for the commercial treatment of copper ore have ever been discovered. COIISGTIGDtly, no eflicient or complete process for t e treatment of copper ore in this manner has ever been worked out.

The present invention is the result of a discovery of these essential facts and vital wherein the treatment of copper ore with S0; solution for the recovery of the copper those skilled in the are.

PROCESS OF TREATING .QOPPER ORES BY LIXIVIATION.

' Specification of Letters Patent- -Pttten1gdS4BPt. li'i 119 38. Application filed September 1, 1916 Serial No. 118,156. I

may be carried out on a commercial scale and which results in a recovery of practi cally the entire copper content of the ore.

In describing the invention, the essential features thereof .will first be set forth, following the order of the several steps of the process, and, next, a description of the process as an entirety will "be given. I

The use-bf a concentrated SO solutioa.

In lixiviating, it is, as I have ascertained, absolutely essential for commercial purposes to employ a. concentrated SO solution. A

concentrated S O 'solution is necessary in order to secure rapid solution of the copper, to prevent. reprecipitation and -the formation "of much CuSO and to obtain a relatively strong copper solution. That these requirements .can be met only by the use of aconcentrated'SO solution is apparent fromfa statement of the following facts :--First, the time required for the solution of the copper is proportionate to the strength of the sol.ution. Second, if a dilute solution is used,

-much reprecipitation occurs in the ulp and CuSO is formed according to the ollowing reaction accede-0&0:cu so oaso cusa Third, the amount of copper which will go into solution, relatively small at best,

is proportionate to the S0 content of the solution, for example: a 6% S0 solution will hold about 2.6% copper; a 5% S0 soluto secure an efiicient absorption of SO large enough towers or other absorption ap era tus must be used and also a suiiicient vo ume of solution. While these present no serious difliculties, the maximum strength of solution which may be secured in a tower or other absorption apparatus is, howeveiynot determined to any great extent by the efiiciency of the apparatus. On the other.

ill)

hand, the strength of the solution depends almost entirely upon the percentage of SO in the gas supplied to the tower and is directly prt-porrgonal to the partial pressure 5 of S0 in the gas entering the tower, '2'. 6., it 216% SS by volume, is supplied to the absorber solution carrying only 6% of maninzuin *ength of solution made front pure SQ could be obtained. F or en- 10 ample, n th t Water at C. and using pure S0 gas, 1 solution carrying about 12% S6 may be cured, but if the gas carry only 18% 6., the richest gases from v a sulfur burner) a solution carrying a little 15 over 2% might be secured, while, if a 6% SOQ be usedelfor example, the gases from a roasting furnace) a solution carrying about {7% might be obtained.

Fro the above, it is obvious that the process cannot be made a success by' applying only dilute roaster gas to the solution, as has been attempted. llelatively strong solutions necessarily cannot be secured from relatively'dilute gases in any absorption apparat I have ascertained that, in order to secure a strong solution of $0,, the dilute gases must first be absorbed in a tovver or other absorption apparatus to form a "eak solution and this weak solution must then so be'o bed in other towers or absorbers to which richer gases are supplied. This is one of the iizzoortant elements of the process of obt' a relatively concentrated S0 solub and process is carried out as follows in the case in which three towers or absorbers used.

" shown the accompanying diagram,

' c1. obta ing the relatively coninvolvii the treatment he fresh Wash solution, es up the loss in the tailings, with the lime needed in the h);-

icipitation passed through ower or absorber and abtogether, they are tower or air ery strong or relatively pure S0 gases are isupplied to this first or strong tower from the boiler and precipitate roaster, hereinafter mentioned. In practising the for-ego lng method, a' strong or relatively concentrate solution 01 SO 16 secured. Further- .niore, all escape involving loss of 550 is cut ofl. Obviously, more than three toiveis 0r absorbers might be used in lllO SllGS, for

example, in the case where gases from different parts of the apparatus tor the treatment of the ore are of such strength that it v would be nlore advantageous to absorb them in separatepa-rts of the absorption appara-.

tus than to mix them before absorption. In most cases, h0u'ever,three towers or absorbers, as' illustrated, are suflicient, though four of thein niight be'used to 'zulmnta where a dilute roaster-gas is supplied to the null.

used, usually by combining With' the copper, and this loss-is made up by supplying practically pure S95 gas to the pulp during agitation. Agitation of the pulp is preferable to ordinary leaching methodsbecausethe copper passes much more rapidly into soluiion. than when leachin is employed. In vlemhing', the fiO 'lirst issolves the copper and then, as thesolutio'n becomesdepleted of its S0 the copper is precipitated, as shown by the foil equation z- 3UL1SQ-i-Qh0:Cu t{) .GLi.SU,+-CuS0 result isa process or solution and precipitatioinnd resolution and reprecipitation; as the solution passes through the charge, thereby forming much copper sulfate (R159 This can'h'e avoided only by an efficient agitation of the pulp while the copper is n to solution. 'lo aroid" repreeipitati and slowing down oi the rate. of solution, very strong or relatively i must be added during the soion process,and add tion of can be done etlecti'vely only While the pulp is being a u it a red.

fi'iciem, separation of the pregnant solution from Hus Moi muted ore.-

The solution must be separated Born the ore Without too much loss of S0 in order avoid reprecipitation. For this purpose, a counter-current system which Will handle the slimes and sands efiiciently necessary. 'During agitation seine 8G is is the bestinethod as the precipitation from" the pregnant solution is complete. Preferably, the barren solution, after the precipitate' has been removed, enters the last l pant solution.

This should be accomplished as rapidly as possible in order to secure a clean crystalline precipitate, and is most efficiently done by the introduction of steam into the solution which not. only heats the solution but also keeps it in violent agitation or ebullition, thereby aiding very materially in the removal of the S0 Precipitation of the copper from the copper sulfate.

In boiling o eration above mentioned copper sulfate is ormed, as represented by the following equation:

4CuSO =C11 SO CuSO +CuSO,+SO The precipitation of the ouso, is one of thei 'nost important features of the process as only about 75% of the copper is precipitated as the cupro-cupric sulfite in an or-- dinary boiling operation, while the remainder, approximately is left in solution as copper sulfate. Precipitation by by electrolysis are out of the question in most laces where the process would be used, and 0 not lend themselves to the process in a satisfactory manner from a metallur- 4o gical standpoint as they would result in the formation of H 80 and more CuSO, which would finally destroy the process, so

far as the recovery ofcopp'er is concerned,

by converting it into a sulfuric acidor sulfate process. It is of great importance that all the copper be secured as the CUPI'O? cupric sulfite and that the sulfate be removed froni the solution. The methodof accomplishing this in the process is extremely simple and eflicient. It consists in the introduction of the proper amount of a lime compound such as lime or limestone into the solution at some time during each cycle of the process, with the result that all the copper is precipitated 'as the red cuprocupric sulfite and the sulfate is removed from the solution as it is formed. The lime or limestone forms calcium bisulfite, Ca(HSO in the strong solution of S0 and vthe calcium bisulfite reacts with the CuSO, to form calcium sulfate and copper sulfite as follows; 7 p I 01180,, Ca (HSQQ CuSO +CaSO, H,SO at It may be provedmathematically .that apmeans of scrap iron, hydrogen sulfid, or

Eyficient removal of the S0 from the ppegproximately enough lime to take care of one third of the copper according to the above equation should be used.

The required amount of lime or limestone may be added with the ore, in the absorption apparatus, or just before boiling. .In most cases, however, it is best 'to add the lime, as previously stated, with'the fresh solution or waterin the safety tower. This results. in cutting off all escape of SO and prevents 7,5" the dilution of the S0 gases with-C0 if limestone is added with the ore, or impoverishment' of the solution in SO if lime or limestone is added with the ore? The -lime or limestone may be added," however, at other stages of the process.

It ma be advantageous to add the finely ground imestone to the hot barren solutionf after the boiling and the cupro-cupric sulfite has settled. out. The'remaining copper may then be precipitated as a green basic sulfate, as shownbelow, mixed with'the calcium sulfate.

This mixed precipitate may be returned to the head of the mill or apparatus for retreatment, or if desired, may be treated separately with a dilute SO solution for the recovery of the copper as. cupro-cupric 'sulfite. If treated with dilute SO solution in large enough quantity all the copper may be dissolved without bringing much of the calcium sulfate into solution. 1

' Another method of carrying. out the recifpitation which has the advantage that 5% o the copper is secured in the pure sulfit'e and only 25% is mixed with the calcium sulfate is to add the lime as a solution of calcium bisulfite to the hot solution, which carries the remaining copper as the sulfate, after the first boiling operation. The remaining copper is then changed to the sulfite, as shown below, and finally precipitated as the cupro-cupric sulfit'e' as the remaining S0 is boiled ofi';

, The place in the cycle at whichth'e limestone or lime is introduced will depend upon the use to which the cop fer'product is to be put and the urity of t e product desired. In any case t e precipitation of the copper will be com lete and all the 00 per will be secured as t e cupro-cupric sul te.

' Roasting of the precipitated white..-

'way. In order'to secure a rich gas and avoid the formation of much CuSO, the roasting operation. should be conducted without access of air. Roasting the precip tate in this manner for ten minutes at 4:00 C. is suflicient to decompose the sulfite and re lease the S0 as shown in the following equation? 3CL1,SO .CuSO lCu ()|-(uSO +5SO To avoid the formation of the CuSO a little carbon is added and roasting without access of air for fifteen'minutes at 600 C.

givesno CuSO but only (M 0 and SO; as

shown by the following equation:

sou so,.ouso,+2c- 9ou o+12so,+co.+oo.

This prevents any loss of sulfur in the precipitate, gives a rich SO gas, and gives the highest grade product possible, excepting the metal. 1

Treatment of tile ealcz'mrt sulfate.

Gomeruatz'on of the heat in'the process.

As much as possible of the heat in the barrensolution from the boiler and settler should be transferred to the pregnant solution before boiling in order to avoid the use of too much steam in the boiling operation. This transfer of heat is readily carried out in a .heat interchangcr through which the solutions ilow in opposite directions in separate compartments separated by conducting Walls. ing walls from the hot barren solution to the cold pregnant solution.

Cooling of the mill solution.

This is absolutel Y necessary in order that the solution may hold the required amount of S9 as the amount of S0 which water will holdin solution dere-ases rapidly with rise in temperature. This cooling is easily done in a cooling tower or other form of cooling apparatus.

The above are the essential steps of the process which is carried out inn general way as follows; 7 V

The ore, ground to the required mesh, usually quite coarse, 1s agitated from fifteen strong tower or absorber.

- in the pulp.

The heat flows through the conduct- ,ered an extension or" the weak tower.

minutes to two hours with the relatively concentrated SO mill solution from the During the agitation concentrated, 2'. e., practically pure SO gas from the boiler or precipitate roaster or both is forced through the pulp to make up for the SQ consumed in dissolving the copper. From the agitator the pulp flows to the decantation and washing or filtering plant Where the pregnant solution is separated from the ore. The pregnant solution then flows to the counter-current heat exchanger, where it absorbs some of the heat from the hot barren solution. From the-heat exchanger, the warm pregnant solution flows to the boiler Where the S0 is expelled by applying steam to the solution. Here all the copper is precipitated as the red cupro-cupric sulfite. From the boiler the hot barren solution carrying the copper sulfite preciiitate and the precipitated calcium sulfate owe to a Spitzkasten or to a flotation cell of any preferred type, Where most of the Ca SOJs separated from the copper precipitate. From the spitzkzsten or cell the hot barren solution flows to the heat exchanger where part of its heat is transferred to the incoming pregnant solution. The partly cooled barren solution next flows to the cooling apparatus and after being cooled to the desired tein perature flows to the last tank or drag of the counter-current decantation and washing system, or to the filtration plant where it is used for washing out the C1130, held Finally, the cooled barren-solution flows to the second or weak absorption tower or absorber. Before passing through this tower or absorber it is joined by the water entering themill to make up the moist-loss in the tailings, etc., this water h 'n first been mixed with enough lime t one t' l0 ot the process and passed through the third or safctytower or Is, to absorb the SO from if ..s escaping from the second tower or absorber. T he mixed solutions pass through the second tower or absorber taking up most of the SQ which is suppliedfrom a sulfur burner or roaster to make u is" the S6 lost in the process From the second tower 01' absorber the solution passes through the first or strong SO; tower or absorber into which the strong gases from the boiler and roa ster, which have not been used up in the agitator, are passed. The residual gases from the strong tower or absorber pass into the weak tower or absorber alon with the relatively weak gases supplied trom the sulfur burner .or roaster and the residual gases from the weak tower pass through-the safety tower or absorber. vhich mi ht he consiri The relatively concentrate SO, solution from.

the strong tower or absorber passes into the agitator along with fresh ore and so on through the mill again. 'The lime needed in the process may not be added in the safety tower, though in most cases this will be advantageous, but may be added as lime or limestone with the ore, to the solution before or after boiling, or as a solution of calcium bisulfite before or after boiling. The place and manner of addition will de- --pend upon local Conditions. The cuprohid cupric sulfite, after being separated from the calcium sulfate formed, is settled or filtered out of the barren solution and sent to the roaster Where it is roasted with the i required amount of carbonaceous material pending upon the nature of the ore, the

point at which the lime or limestone is added, and the particular kind of apparatus used in the different. departme tsi of the mill. v

As is readily seen from the above brief description, the process difiers from all other processes, which aim to use a solution of S0, for the treatment of copper ores, in all the divisions or parts of the process givenbelow, each of which parts is an im-' provement over the older processes. It

should also be noted how efi'iciently each of these steps links with the others to make a complete process in every detail.

' These improvements are the followin The use of a relatively concentrated S solution, the lack of which renders the process cumbersome, incflicient and impracticable, and which cannot be secured from dilute gases in the manner hitherto used. The

. manner of securing saidrelatively concentrated 80 solution by subdividing the absorption apparatus and supplying gases of of the absorption apparatus in order to different strengths to thedifi'erent sections of the apparatus as described. The use of the concentrated gases from the roasting and boiling operatlons in a separate sect on secure the strong solution needed. The use of lime or limestone in the process in order to secure all the copper in the form of a cupro-cupric sulfite precipitate, a very vital part Ofthe sulfite process and the lack of v which was one of the main causes of failure in previous attempts to use this-solvent. The'use of the limestone or lime in the process removesthe sulfate from the solution, which, if notremoved, means the destruction of the process as a sulfite process. As will be noted. from the foregoing description,

either limev or limestone may be used and may be added at any point in the cycle of treatment and the result will be that all the copper will be precipitated as the cuprocupric sulfite and the sulfate will be removed from the solution as calcium sulfate. Thus, the lime compound maybe added with the ore, may be added in the absorption apparatus, may be added to the pregnant solution, may be added to the hot solution from the boiler and the precipitate formed returned for retreatment. result is the same, e., the copper is all secured as the cupro-cupric sulfite precipitate and the sulfate is removed from the solution. From a chemical standpoint it makes little difference at What point the lime or limestone is added as to its use for the above purposes. Ah is readily seen it may be advantageous to add the limeor limestone at some particular point for other reasons and in most cases it Will be found advantageous to add it as mentioned in the next item, the use of the lime or limestone needed in the process in the absorption apparatus as described to prevent loss of S0,, The rqasti gof the sulfite precipitate as described' in' order to secure a richSO gas, prevents loss of sulfur, and secures the richest copper product possible.

It should be here noted that this roasting operation utilizes some newly discovere properties of the cupro-cupric sulfite: -the separation of the calcium sulfate from the sulfite precipitate, an important item if a very high grade product is desired or if freight and hauling charges are very high;

the heating of the pregnant solution by the transfer of heat from the htt barren solution in order to avoid too much dilution with steam in the boiling operation and also to conserve the heat as much as possible; the special cooling of the solution without which it would be impossible to secure the relatively concentrated SO solution needed. From the above description the simplicity and efficiency of the process are apparent,

the most noticeable features being the small chemical cost, the completeness of the precipitation, and the high grade product. The special applicability of a counter-current system to the separation of the pregnant solution from the ore and the washing of the tailings is also an item of interest. Tests of the process have given most excellent re-' In each case the.

sults, some oxidized ores yielding as high as 99% of the copper in a fifteen minute treatment and giving a product carrying over 85% copper. Roasted sulfid also gives good results. The relatively low cost/of the plant necessary for the process, and

the simplicity and cheapness of operation, I due to the relatively coarse grindingneces- I sary, the short time of treatment, and the completeness of the precipitation, and the simple roasting operation necessary, are readily appreciated when a plant is bemg designed. v I

Though I have described a preferred way of carryingout the process, I do not wish to be limited by the brief outline possible in a patent Specification; as it .is evident that a great many, minor changes might be made without altering the main features of the process. I, therefore. desire to be limited as to the different steps and the process as a whole onlyby the description as interpreted in the appended claims. No drawings are given asthe process is not dependent in any of its divisions 'upon any particular form of apparatus, and the descriptiongiven is sufficiently clear and detailed that any competent metallurgist or any one familiar with the-art of metallurgy in any detail. can apply the process to, any ore to which it is suited.

lVhat is claimed is:-

1. The process which consists in liXiviating copper orcs with a concentrated S0 so lution'made by first bringing the solution in contact with .rtiatively weak S0 uses and then successively bringing the same solution in contact with successively stronger SO 'gases in separate absorbers 2. A copper ore treating process wherein the precipitate is roasted and the S0 gas driven-off, which consists inagitating the ore in a concentrated solution of S0 gas and passing very strong SO gases from the precipitate roasting operation of the process through the pulp during said agitation and thereafter absorbing the 1 remaining SO in said strong gases in a relatively weak S0 solution and in enriching said solution to make theaforesaid concentrated S0 solution for the treatment of more ore.

A copper ore treating process wherein the pregnant. solution is boiled to efl'eot precipitation and production of S0 gas, which consists in agitating the ore in a con centratedsolution of S0 and passing the practically pure S0 gases from the boiling,

operation of the process through the pulp during said agitation and thereafter absorbing the remaining SO in said gases in a relatively weak SO solutionand in en riching said solution to make the afore said concentrated S0 solution for the treatment of more ores.

LA copper ore treating process wherein the pregnant solution is boiled to effect pre- .oipitation and production of S0 gas and the precipitate roasted and S0 gas driven off, which consists in agitating the ore in a concentrated solution of S0 and passing the very strong gases from the precipitate roasting operation and the practically'pure SO gases from the boiling operation of the na /sees l per ores with an SO solution for the recovery of the copper which consists in addinga lime compound to the mill solution during the process in order that all the copper may be secured as copper sultite.

S. The step in the process of treating copper ores with an S0 solution for the recovery of the copper which consists in adding a lime compound to the mill solution during the process in order to secure all the copper as copper sultite and to precipitate the sulfate as calcium sulfate and add-' ing said lime compound at the exit end of the S0 absorption system in order to prevent loss of S0 9. The process of treating successive batches of copper ores with an S6 solution for the recovery of the copper; which consists in lixi'viating the successive batches of ore with the solution and in adding enough of a lime compound during each successive use to cause substantially all the copper to be precipitated from the pregnant solution cium sulfate when the excess S0 is removed from. the pregnant solution.

11. In the process of treating copper ores with the cycle use of an SO solution for the recovery of the copper wherein the S0 solution, is enriched by the absorption of SO gas during each cycle of use the addition of enough of a lime compound during each cycle of use to cause substantially all the copper to be precipitated as a copper sulfite compound and substantially all the sulfate com-v bined with copper to be precipitated as cal 'cmm sulfate when the excess SO isremoved from the pregnant solution, said lime compound being added at the head of the absorption system in order to prevent loss in" sm. v I

12. The process of treating copper ores for the recovery of the copper, which consists in roastin copper sulfite precipitate without access of air, passing the very strong SO gases. from this roasting operation through thesolution and ore during agitation of the latter and then bringing said gases in contact with a relatively dilute SO duction of the S0 vapor.

' 14. The process of treating copper ores for the recovery of the copper, which consists in'roasting ,the' copper sulfite precipitate without access of air and in, the presence of carbonaceous material, passing the very strong SO gases from this roasting opera tion through the solution and ore during agitation of the latter, and then'bringing said gases in contact with a relatively dilute SO solution to make aconcentrated'solution for the lixiviation of more ore..

15. The process of treating copper ore for the recovery of the copper, each cycle of which consists in making a relatively dilute SO solution by bringing cold barren solution in contact with relatively dilute SO, gases supplied to the process from an external source, making a concentrated SO solution by bringing aforesaid relatively dilute solution in contact with very strong SO gases from the roastin and boiling operations after said gases ave been passed through a mixture of concentrated solution and ore while said mixture is being agitated, lixiviating ore by agitating it with first mentioned concentrated SO solution, passing very strong SO gases from the roasting and boiling operations through last said ore and solution while they are being agitated,

separating the pregnant solution from the lixiviated ore, heating said pregnant solution by transferring heat to it from hot barren solution, boiling oif the excess SO from aforesaid. heated pregnant solution and precipitating the copper as a copper sulfite compound, separating said -,precipitate from the hot barren solution, roasting said precipitate without access of air and in the presence of carbonaceous matter, passing the gases from the roasting and boiling operations on for further use in'the process as described, cooling the last mentioned barren solution by transferrin some of its heat to pregnant solution, furt er cooling said barren solution by contact witha current of arr, passing said cooled barren solution on for use in the 'ngxt cycle of the process,

and adding a lime compound to the solution duringeach cycle of the process. 5

16. The process of treating copper ore for the recovery of the copper, each cycle of whlchconsists in making a relatively dilute SO solution by bringing cold barren'solution containing a lime compound in contact with relatively dilute SO gases supplied to the process from an external source, making a concentrated SO solution by bringing aforesaid relatively dilute solution in contact with very strong SO gases from the boiling androasting operations after said gases have been passed through a mlxture of concentrated SO solution and ore while said mixture is being agitated, lixiviating ore by agitating it with the first mentioned concentrated SO solution, passing very strong SO gases from the roasting and boiling operations through said ore and solution while said ore and solution are being agitated, separating the pregnant solution from the lixiviated ore, heating said pregnant solution by transferring heat to it from hot barren solution, boiling off the excess SO from the aforesaid pregnant solution and precipitating the copper as a copper sulfite compound, separating said precipitate from the hot barren solution, roasting said precipitate without access of air and in the presence of carbonaceous matter, passing the gases from the roasting and boiling operations on for further use in the process as described, cooling the last mentioned barren solution by transferring some of its heat to pregnant solution, further cooling said barren solution by contact with a current of air, adding a lime compound to said cooled barren solution, and passing on said barren solution containing said lime compoundfof' further use in the next cycle of the process.

17. The process of treating copper ore,

which consists in lixiviating the ore with a concentrated ibO" solution, separating from the lixiviated ore the pregnant solution thereby obtained, boiling the pregnant solution to drive off SO from the pregnant solution and effect precipitation of the copper as cupro-cupric sulfite, and roasting the precipitated cupro-cupric sulfite Without access of air to drive off the S0 from the copper.

18. The improvement in the art of treating copper ore for the recovery of the copper, which consists in lixiviating the ore with a concentrated S0 solution to which has been added a lime compound, adding S0, to the ore and solution duringthe lixiviation, agitating the ore and solution during the lixiviation, separating from the lixiviated ore the pregnant solution thereby obtained, and driving off the S0 from the pregnant solution, thereby effecting precipitation of the copper as cupro-cupric sulfite.

19. The improvement in the art of treating copper ore for the recovery of the copper which consists in lixiviating the ore with a concentrated SO solution to which has been added a lune compound, adding SO to the s, driving oil the S0 from the pregnant so1uore and solution during the lixiviation, agi

tating the ore and solution during the 11X- iviation, separating from the hxivlated ore the pregnant solution thereby obtained,

tion thereby efiecting precipitation of the copper as cupro -cupric sulfite, separating concentrated SO solution and passing c0ncent-rate SO gas into theme and solution during the agitation thereof.

21. The improvement in the art of lix iviating copper ore With an SO solution which consists in adding a lime compound whereby all the copper is precipitated as cupro-cuprie sulfite. I

22. The step in the art of treating copper ore for the recovery of the copper which consists in roasting cupro-eupric sulfite with carbonaceous material and Without accessof air.

23. The process of treating copper ore, which consists in lixiviating the ore with aconcentrated SO solution, separating from the lixiviated ore the pregnant solution thereby obtained, boiling the pregnant solution to drive off SO from the pregnant solution and effect precipitation of the copper as cupro-eupric sulfite, and utilizing the hot barren solution to heat the pregnant solution before the boiling operation.

24. The process of treating copper ore,

which consists in lixiviating the ore with a concentrated S0 solution, separating from the lixiviated ore 'the pregnant solution thereby obtained, boiling the pregnant solution to drive off S0 from the lnrgnant solution and effect precipitation of the copper as cupro-cupric sulfite, and effecting a heat transfer between the hot barren solution and the pregnant solution before latter.

NIELS C. CHRISTENSEN.

V /itnesses A.- M. CHENEY, LOUISE WEEK.

boiling the 

